Third generation pantograph device for stretching a thermoplastic film simultaneously in the longitudinal and transverse directions

Abstract

A device for stretching a thermoplastic film simultaneously in the longitudinal direction and the transverse direction is provided. The device includes, on each side of the film (F) to be stretched, grasping members for grasping a lateral edge of the film (F), and guide members; first and second guide rails (R1, R2), on which the members and are respectively able to move; first connecting rods connecting the grasping members and the guide members. In an embodiment, each guide member is connected to a single grasping member by one or several of said first connecting rods, and is connected to a first longitudinal adjusting member by one or several second connecting rods connected to the first longitudinal adjusting member; and the device includes adjusting means for adjusting the position and orientation of said first longitudinal adjusting member relative to said first and second guide rail (R1, R2).

What is claimed is: 
     
       1. A device for stretching a thermoplastic film simultaneously in a longitudinal direction of the film and a transverse direction of the film, the device comprising, on each side of the film to be stretched,
 grasping members for grasping a lateral edge of the film, in particular in the form of clamps;
 a first guide rail and a second guide rail positioned one along the other, the first guide rail being closer to the film than the second guide rail, the grasping members being placed on the first guide rail and the grasping members being able to move along the first guide rail; 
 
 guide members, the guide members being placed on the second guide rail and are able to move along the second guide rail, the second guide rail being connected to said first guide rail such that its position is not adjustable relative to said first guide rail in a direction transverse to the film; and 
 first connecting rods connecting the grasping members and the guide members, the first connecting rods being movable relative to the grasping members and the guide members along first axes; 
 wherein, on each side of the film,
 the device further comprises a first longitudinal adjusting beam, the length of which is such that the first longitudinal adjusting beam extends over a series of consecutive grasping members and consecutive guide members; 
 each guide member is connected to a single grasping member by one first connecting rod or by several first connecting rods superimposed on each other, and is connected to the first longitudinal adjusting beam by one second connecting rod or by several second connecting rods superimposed on each other, wherein:
 the first longitudinal adjusting beam extends along the first and second guide rails; 
 wherein each of the second connecting rods has a first end connected to a single guide member and a second end connected to said first longitudinal adjusting beam, said first end being movable relative to the single guide member and said second end is connected relative to this first longitudinal adjusting beam along a second axis parallel to said first axes; 
 wherein each second connecting rod(s) of a first guide member and each second connecting rod(s) of a second guide member consecutive to said first guide member are connected to said first longitudinal adjusting beam at pivot points that are combined on this first longitudinal adjusting beam; and 
 wherein the device includes assemblies comprising the first longitudinal adjustment beam connected to one or more screws via one or more posts, the one or more screws configured to allow for adjusting the position and orientation of said first longitudinal adjusting beam relative to said first and second guide rails, said assemblies being arranged at intervals along the length of the first longitudinal adjusting beam and configured to move portions of the first longitudinal adjusting beam connected to said assemblies in a direction perpendicular to a direction of advance of the film. 
 
 
 
     
     
       2. The device according to  claim 1 , wherein, on each side of the film, the device comprises:
 a second longitudinal adjusting beam extending along the first and second guide rails, homologous to said first longitudinal adjusting beam and such that the second longitudinal adjusting beam extends over a series of consecutive grasping members and guide members, and 
 a series of connecting rod corresponding to said second connecting rods, 
 the second longitudinal adjusting beam and the series of connecting rods being situated on a side that is opposite a side of the grasping members, the first connecting rods, and the guide members on which said first elongated adjusting beam and the series of said second connecting rods are located. 
 
     
     
       3. The device according to  claim 1 , wherein each of the second connecting rods of the second guide member consecutive to said first guide member extend between the two said first connecting rods associated respectively with the first and second guide members. 
     
     
       4. The device according to  claim 3 , wherein said first longitudinal adjusting beam is in the form of a rail with an upside down U-shaped section, forming a first guide slot, and wherein the second ends of the two second connecting rods are linked to a first pivot which is guided by said first guide slot, the first guide slot and first pivot thus connecting the two second connecting rods to the first adjusting beam. 
     
     
       5. The device according to  claim 1 , wherein each of the second connecting rod(s) of the first guide member and the each second connecting rod(s) of the second guide member consecutive to said first guide member extends over a side of said second rail opposite said first rail. 
     
     
       6. The device according to  claim 5 , wherein said first longitudinal adjusting beam is in the form of a rail, having guide parts engaged on it and movable on it, each of the guide parts being secured to a pivot on which said second connecting rods are pivotably mounted. 
     
     
       7. The device according to  claim 1 , wherein the device further comprises a first linear motor associated with said first longitudinal adjusting beam acting on each junction point of said second connecting rods so as to assist a movement of the second connecting rods said first longitudinal adjusting beam during the longitudinal stretching operation of the film. 
     
     
       8. The device according to  claim 1 , wherein the one or more screws traverses the first longitudinal adjusting beam and a flank of a base of the first and second guide rails, such that the screw is rotatable relative to the flank, wherein a rotation of the one or more screws moves the first longitudinal adjusting beam perpendicular to the direction of advance of the film. 
     
     
       9. The device according to  claim 2 , wherein the second longitudinal adjusting beam is in the form of a rail with an upside U-shaped section, forming a second guide slot, and wherein ends of two consecutive connecting rods of said third connecting rods are linked to a second pivot which is guided by said second guide slot, the second guide slot and second pivot thus connecting the series of connecting rods to the second adjusting beam. 
     
     
       10. The device according to  claim 2 , wherein the device further comprises: a second linear motor associated with said second longitudinal adjusting beam acting on each junction point of said series of connecting rods so as to assist the movement of the series of connecting rods along said second longitudinal adjusting beam during the longitudinal stretching operation of the film.